Mineral fiber products, particularly products made of glass fibers, are typically made as either continuous fibers or discontinuous fibers. Various organic coatings can be applied to these fibers for protecting the fibers from abrasion, for connecting the mineral fibers to each other to form a structural product, and for providing compatibility of the mineral fibers with other materials, such as the compatibility between the reinforcement fiber and a plastic matrix. In the case of insulation products, the mineral fibers are usually bonded together by organic material, such as a phenol/formaldehyde binder, to form a spring-like matrix which can recover after compression during packaging. One mat product having both glass fibers and fibers of organic material, and manufactured by a textile non-woven process, is disclosed in U.S. Pat. No. 4,751,134 to Chenoweth et al.
The application of organic material to the mineral fibers can take several forms. Continuous mineral fibers can be run through a bath or across a coater to apply a coating to the fibers, such as during the application of a size to continuous fibers. Alternatively, the organic material can be sprayed onto the mineral fibers. This method is commonly used in the manufacture of insulation products with a rotary process where a cylindrical veil of mineral fibers is met with the sprays of the phenol/formaldehyde binder.
One of the problems with applying aqueous organic binders of the prior art to cylindrical veils of mineral fibers is that a portion of the binder tends to evaporate prior to contact between the liquid binder drop and a mineral fiber in the veil. This problem is exacerbated by the need to apply the binder relatively close to the fiberizer, i.e., where the hot environment is particularly likely to cause some of the liquid binder droplets to evaporate before contacting a glass fiber. The evaporated binder material becomes a contaminant in the exhaust air stream of the process and must be cleaned up in order to avoid pollution problems. Also, the binder material on the mineral fibers tends to be sticky, requiring extensive cleaning of the fiber collection apparatus to prevent the build-up of clumps of glass fiber insulation material which can drop into the product and cause a product defect. Further, the binder material must be cured in an oven, requiring tremendous energy not only for curing the binder itself, but also for driving off the water associated with the binder, and for environmentally cleaning the gaseous by-products of the heating and curing process.
Attempts have been made in the past to integrate organic binder materials with mineral fibers from a rotary process without merely spraying the veil of fibers with an aqueous solution of the binder material. For example, U.S. Pat. No. 5,123,949 to Thiessen discloses a rotary fiberizing process where additive particles are supplied through the hollow quill or axle of the rotating spinner. The particles are directed toward the veil of mineral fibers from a locus within the veil. The additive particles can be fibrous in nature, such as cellulose fibers, and also can be resinous material in a particulate form.
Another approach in integrating organic material with rotary mineral fibers is disclosed in U.S. Pat. No. 5,614,132 to Bakhshi et al. A glass rotary fiberizer is operated to produce a downwardly moving hollow veil of glass fibers, and a polymer fiberizer is operated within the hollow veil to produce polymer fibers within the veil but directed radially outwardly toward the glass fibers. The polymer fibers commingle with the glass fibers, producing a reinforced resinous product having both glass fibers and polymer fibers. While the process of the Bakhshi et al. patent is effective for making certain products, it can be desirable in certain instances to move the polymer fiber forming environment further from the intensive heat of the mineral fiber forming environment.
For example, an alternative to the coaxial rotary commingling process, U.S. Pat. No. 5,595,584 to Loftus et al. discloses an alternate commingling process where glass rotary fiberizers centrifuging glass fibers, and polymer rotary fiberizers centrifuging polymer fibers, are positioned alternately with each other arranged along a collection surface. The polymer fiberizer can be oriented at an angle to the vertical so that the flow of polymer fibers is directed at an angle into contact with the veil of glass fibers. While the purpose of the alternate commingling process was to decouple the polymer fiber forming environment from the glass fiber forming region, it was perceived to be quite difficult to uniformly integrate the rotary-formed polymer fibers into the veil of glass fibers. The nonuniformities of the rotary polymer process combined with the swirling, chaotic environment of the glass fiber forming region would prohibit significant penetration of the polymer fibers into the glass fibers, potentially resulting in an unpredictable, laminar product having less than desired properties for some products.
It would be advantageous if there was developed an improved process for integrating polymer or other organic fibers into a flowing stream of glass fibers to produce a generally uniform mix of glass fibers and polymer fibers, preferably uniform by fiber distribution and uniform by weight. Such a process should provide protection for the polymer material supplied in fibrous form so that the fibers are not subjected to a hot environment which could undesirably vaporize the polymer material or otherwise degrade the polymer material, or which could soften or melt the polymer fibers into non-fibrous particles.